The use of disposable patterns consisting of films is known from German Offenlegungsschfirt No. 1,926,163. For the production of these patterns the films are shaped to correspond to the required casting by means of a known deepdrawing shaping process utilizing reduced or elevated pressure. The patterns are provided with a rim which extends therearound and which lies in the mold divison plane, this rim lying on the edge of the foundry molding box (also known as a mold member) after the pattern has been introduced into the latter. The foundry molding box is then filled with loose, binderless sand. In the case of a frame-like molding box, a film is also laid on the opposite side of the molding box and the interior of the latter is then evacuated. Through the external air pressure applied to the films, the latter are pressed against the sand. In this way it is possible to produce patterns of stable shape from very thin films. This known method of molding is decidedly advantageous because the production of the patterns entails only little expense, a casting having a very smooth surface is obtained, and no preparation of the sand is requried. All that is required to remove the casting from the mold is to terminate the reduced pressure in the foundry molding box.
A prerequisite for the application of the process described above is that the reduced pressure in the foundry molding box should be maintained from the time when the pattern is complete until the casting has completely cooled. In order to make this possible, it is known for the foundry molding box, that is to say the upper and lower parts of the box, to be provided with the individual flexible vacuum pipes. For individual production this does not constitute a great disadvantage, although manipulation of the molding boxes is limited.
For continuous production the molding boxes are placed on trucks of a closed-circuit rail conveyor which brings the molding boxes to the individual stations. The major part of the time required for one circuit of a rail conveyor truck, that is to say for the production of a casting is required for the cooling of the casting. The longer the rail conveyor, the longer the cooling time available for the same cycle sequence. In known rail conveyors, in which the foundry molding boxes are connected to vacuum pipes, the length of the rail conveyor is however mainly limited by the possible length of the vacuum pipes. These pipes, which must be of flexible construction in order to enable the molding boxes to be manipulated, have been found liable to breakdown and to be a very great hindrance. It is known for a rail conveyor to be made in the form of a circle and for all the vacuum pipes associated with the molding boxes to be joined to a centrally disposed vacuum pipe. These known rail conveyors have the additional disadvantage that they require considerable space.
It is an object of the invention so to construct a rail conveyor of the kind first-mentioned above that it can be made of any desired length, that it can be in the form of a space-saving arrangement, and that unrestricted manipulation of the foundry molding boxes is retained.
According to the invention there is provided a rail conveyor having a plurality of rail conveyor trucks coupled together to receive foundry molding boxes connected by vacuum pipes, characterized in that each rail conveyor truck is connected by a vacuum pipe to the two neighboring rail conveyor trucks coupled to it, that a foundry molding box placed on a rail conveyor truck is adapted to be coupled by a connector to the vacuum pipe of the rail conveyor truck and that the vacuum pipe connecting the rail conveyor trucks is provided at predetermined intervals with couplings, which are closed by non-return valves for the intermittent connection of at least one vacuum pipe connected to a vacuum pump. At predetermined intervals the vacuum pipe of the rail conveyor truck is provided with couplings for the connection of an evacuation pipe, which is connected to a vacuum pump. This evacuation pipe is intermittently connected, in dependence on the timed advance of the rail conveyor trucks, to the couplings disposed one behind the other. The evacuation pipe therefore does not need to follow the entire path of the rail conveyor trucks, but is moved to-and-fro only over a small part of that path, corresponding to the timed movement of the rail conveyor trucks.
In one embodiment of the invention the couplings of the vacuum pipe of the rail conveyor trucks are connected to two evacuation pipes, one of which is coupled only when the rail conveyor trucks are stationary and the other during the timed movement of the rail conveyor trucks, to respective couplings. The use of two evacuation pipes provides the advantage that the vacuum pipe of the rail conveyor trucks is always connected to at least one evacuation pipe.
The two evacuation pipes are provided with a drive which permits displacement of the coupling elements of the evacuation pipes perpendicularly to the direction of movement of the rail conveyor trucks. The evacuation pipe participating in the displacement of the rail conveyor trucks is additionally provided with a drive which permits movement of the coupling element of the evacuation pipe parallel to the direction of movement of the rail conveyor trucks. The connection of the evacuation pipes to the couplings of the vacuum pipe of the rail conveyor trucks and their uncoupling are effected entirely automatically.
Each rail conveyor truck is provided with a control valve, by which the foundry molding box can be shut off from the vacuum pump. The valve may be controlled by means of electric or mechanical contacts. The purpose of this control valve is to shut off the foundry molding box from the vacuum pump of the rail conveyor trucks when the casting has cooled sufficiently to enable it to be removed from the mold. It is also conceivable for the control valve to be in the form of a two-way valve, so that the foundry molding box is supplied with air simultaneously with the shutting off of the vacuum supply thereto.